If tenant advised would affix step to mobile home, did not do it and did not advise it was not done, then got hurt can he sue

Yes, if your renter told you of a danger and issue to the steps and you did not fix it, and they were injured because of this, yes they can sue. Which is why of course as a landlord I am sure you carry liability insurance on your property

We tore off back porch, was late in day and tenant advised would put steps back up next day, he never did and I was never advised me that it was not done.

... can he sue [?]

Yes, certainly.

Can he recover? That's another question. Your attorney, paid for by your insurance carrier, will certainly raise the issue that the tenant failed to install the steps or to tell you that he didn't.